Before we begin I would like to say that this guide is based off of vinster's truetrophies trophy guide so if you're looking for some more Sifu help please consider checking out some of his guides!
The goal of this achievement is to get a score of 5,800 or higher
The level I completed this on was Arena pack 2 Level 1 "Ruthless"
The most important thing you'll need for a good score is your multiplier which means that you're going to have to avoid getting hit as much as possible. However, if you do get hit all is not lost, the focus move "calbot" actually increases your multiplier by an entire point (x1 to x2 Or x2 to x3) so if you need to get your multiplier back up calbot is a great way of recovering.
In addition to having a score multiplier, you're going to need to vary your moves. What I found works best for me personally is rotating between charged backfist (hold Y), crotch punch (up, up, X), raining strikes(Y, PAUSE, Y), and sweep (down, up, Y) followed by a double punch attack on a downed enemy. My moveset was not necessarily in that particular order, I just happened to use that set of moves. If you have another set of moves you like then use that set. You just want to make sure you're not repeating moves to often.
Finally, try finishing enemies when you can. I believe that it gives you more score but I am not 100% sure.
This achievement can be a little frustrating to achieve so just remember to always block early to avoid hits, use calbot when you do get hit, and vary your moveset enough to get a good score.
EDIT: Huge thanks to | King Leo | for the fantastic score grinding method, check out his comment below on how to perform it for some free early score!